A display apparatus such as a liquid-crystal display incorporates therein a light source apparatus in the form of a backlight thereof. As examples of light sources forming the light source apparatus includes a fluorescent lamp including a phosphor particle layer containing a plurality of phosphors. Specifically, fluorescent lamps include a cold cathode fluorescent lamp (Cold Cathode Fluorescent Lamp; CCFL) and a hot cathode fluorescent lamp (Hot Cathode Fluorescent Lamp; HCFL) (for example, see Patent Document 1).
An example of a related-art phosphor particle layer includes a blue light-emission phosphor BaMgAl10O17:Eu (called BAM:Eu), a green light-emission phosphor LaPO4:Ce,Tb (called LAP), and a red light-emission phosphor Y2O3:Eu (called YO) as a plurality of kinds of phosphors.
It should be noted that a compositional formula of each phosphor indicates a host material and a luminescent center. For example, in the aforementioned BAM:Eu, a portion of BaMgAl10O17 represents a host material, and a portion of Eu represents a luminescent center. When the blue light-emission phosphor is expressed by BAM:Eu, a concentration of a luminescent center can optionally determined.
The blue phosphor BAM:Eu has been widely used because the BAM:Eu includes a high luminous efficiency; however, in recent years, since members (color filters, optical sheets, etc.) forming a display apparatus has an improved performance, and hence the display apparatus can finally output light having a certain brightness or higher, it may not be necessary to select a phosphor with a priority of a luminous efficiency.
However, although the BAM:Eu is the blue light-emission phosphor, BAM:Eu,Mn dissolving Mn shows green and a blue light-emission phosphor not dissolving Mn contains much of light in a green region. That is, it is difficult for the BAM:Eu to exhibit excellent in color purity of a blue region.
In contrast, attention has been drawn to another blue light-emission phosphor (Srx,Bay,Ca(1-x-y))5(PO4)3Cl:Eu (where 0≦x, y≦1 and x+y≦1); that is, a so-called SCA. As shown in FIG. 5, an emission spectrum (solid line a) of the SCA has a steep spectrum shape with a narrow half width as compared with an emission spectrum (dot and dash line b) of the BAM:Eu. That is, the SCA exhibits excellent blue with high color purity as compared with the BAM:Eu.
However, having conducted extensive studies, the inventors of the present invention have pointed out that a specific problem; that is, a luminescent chromaticity a change in time in a fluorescent lamp containing a SCA on a phosphor particle layer.
In order to examine a change in luminescent chromaticity, a first CCFL and a second CCFL are prepared, each of which is incorporated in a display apparatus, and a change in chromaticity is measured in the display apparatuses having respective CCFLs. The first CCFL includes SCA, BAM:Eu,Mn and YVO4:Eu as phosphors, and the second CCFL includes BAM:Eu, BAM:Eu,Mn and YVO4:Eu as phosphors.
The first and second CCFLs are incorporated into backlight (light source apparatus) of 32-inch liquid-crystal displays, respectively. Then, a change in chromaticity on the surfaces of the respective displays is measured. The change in chromaticity is normally observed after turning ON the power of the display. The change in chromaticity (Δx, Δy) is measured after three seconds from turning the power ON, and the resulting chromaticity is evaluated in a duration from an onset to 120 seconds after the measurement.
The results show that a change in chromaticity of the first CCFL is (Δx=+5/1000, Δy=−33/1000) and a change in chromaticity of the second CCFL is (Δx=0/1000, Δy=−8/1000). That is, the change in chromaticity obtained after 120 seconds in the liquid-crystal display using the SCA as the blue light-emission phosphor is larger than that in the liquid-crystal display using the BAM:Eu as the blue light-emission phosphor. In particular, a significantly large change in y value is observed in the liquid-crystal display using the SCA.
As described above, if chromaticity (initial chromaticity) of the fluorescent lamp continues to change immediately after light emission is started, output image information continues to deteriorate due to fundamentally unrelated factors to the image information in the display apparatus having the fluorescent lamp as a light source. The image with such deterioration exhibits unnatural image as a whole.
Accordingly, instability in the fluorescent lamp forming the light source of the display apparatus may cause adverse effects on images through deterioration of image information in the display apparatus, such as unpleasant impression given to viewers who eventually watch such images.    [Patent Document 1]: Unexamined Published Japanese Patent Application No. 2005-332625